I think this is the part of game when devs can cooperate with fans .. just little demonstration

there would be probably time to "fix" something..
For me - I would do that this way:
- only potions can be drinked (I am talking about fight, not about drinking sessions with Yarpen
)
- mutagen means permanent improvement ... they should be rare and for example there can be some fun with combination ... stronger/weaker mutagens (more weaker = one stronger) or combination of abilities (defence, poison resistance ... and again combination or two of same sort to get bonus,...)
- heavy/light potion system: you will have two kinds of potions:
- - weaker, usual p.: cat, swallow,... >> you can make them from herbs/common ingredients, low toxicity, weaker impact, you can drink them any time
- - stronger, rare p. >> more difficult to find ingredients, maybe higher toxicity, stronger impact, you can drink them only before fight (meditation,...)
- impact of potions comes immediately and there will be normal system - time of effect
This is just my idea, how I would do that, but I don't want to criticize TW3 system since I did not see it yet, but I am just afraid it will be too late, when game will be already out.
FAQ

... Yes, I have faith in CDPR, but I also consider this as part of the game which we can decide together with no need to hide it until game will be finished.